The present invention relates to display devices for displaying images on liquid crystal displays, and particularly to a display device having means for making on-screen display, and a display method for the display device.
Since a display device of the active matrix type such as liquid crystal has features of small depth, light weight and low consumption power, it is also used as a display device for digital still cameras and digital video cameras. Above all, in order for the whole system to achieve the low cost and high picture quality, the display device is demanded to have the interface to the general-purpose digital format.
The Recommendation ITU-R BT. 656-4 known as a specification of the standard digital-format video signal defines a digitalized NTSC/PAL video signal of the interlaced scanning type in which the group of even lines and group of odd lines of each frame are alternately displayed.
In addition, the color format described in the Recommendation ITU-R BT. 656-4 is the format of YUV 4:2:2 formed of luminance information Y and two different pieces, U and V of color-difference information. The luminance information Y is given to each pixel, but the color difference information U, V is compressed to half as much for one of each two pixels.
On the other hand, most of the monitors for the digital still cameras and digital video cameras and display devices for television receivers have the on-screen display (hereinafter, referred to as “OSD”) function incorporated and used to display the current status and the post-adjustment status of image in order for the user to make the adjustment of the image position, image quality and so on. This OSD function is now actually built into the signal processor LSI in order to facilitate conversion of resolution and image processing.
The display device having the interface to the digital video of YUV format has the OSD function provided in the signal processor LSI from which the processed signal is transferred to the display. In other words, the YUV video signal such as the camera signal or broadcast video signal from the imaging device or recording media is transferred to the display device together with the OSD signal of YUV format to which an OSD signal was converted. Therefore, the display device receives the YUV video signal and YUV OSD signal, and converts those signals to the RGB (Red, Green and Blue) video signals for driving the liquid crystal so that they can be displayed on the liquid crystal display panel.
In addition, an example of the display device capable of making OSD is proposed as, for example, in U.S. Pat. No. 6,664,970 (JP-A-2001-42852). In this example, a control unit is used to judge the resolution of the input video signal from the horizontal and vertical synch signals fed together with the input video signal. A resolution converter is provided to convert the resolution of the input video signal on the basis of the resolution found by the control unit to conform to that of the display device. The resolution converter also generates the horizontal and vertical synch signals and pixel clock signal synchronized with this resolution-converted video signal. In addition, an OSD generator is provided to produce an OSD signal in synchronism with those generated horizontal and vertical synch signals and pixel clock signal. Moreover, an OSD mixer mixes this OSD signal and the resolution-converted video signal, and they are displayed in combination on the display panel.